B. Pertissis adenylate cyclase was activated by calmodulin in a dose-dependent fashion. Fifty percent of maximal activation was obtained at a concentration of 0.6 nM calmodulin. Calmodulin activated the enzyme system 10-20 fold of the basal enzyme activity. Unlike the mammalian enzyme system, this enzyme was able to convert all of the substrate ATP to cyclic AMP. Utilizing this aspect we have been able to follow this enzyme reaction rate with UV spectrophotometer 31p-NMR. We have been able to demonstrate the formation of 5 feet AMP and pyrophosphate along with the disappearance of ATP. Halothane inhibited the calmodulin activated adenylate cyclase in a dose dependent fashion. Fifth percent inhibition was obtained at about 30 mM of halothane. This inhibition of halothane was not altered by calmodulin concentrations. Deuterated halothane also inhibited the calmodulin activated adenylate cyclase almost to the same extent as halothane. Thus showing that deuteration of halothane has no effect on this system. Beef heart phosphodiesterase was activated 2-3 fold by calmodulin (50% of maximal activation was obtained at 6 nM. Halothane inhitibed the enzyme system to much less extent than the adenylate cyclase (at 6 nM colmodulin 30 nM halothane inhibited 40% of calmodulin activated phosphodiesterase while 54 nM halothane caused 50% inhibition). Deuterated halothane indicating again that deuterium of halothane had no effect on the biological activity of halothane.